1. Field of the Invention
The invention relates to a selective freewheeling mechanism. The selective freewheeling mechanism is intended in particular for an electromechanical vehicle brake, in order to expand it into a parking brake. The invention also relates to an electromechanical vehicle brake having the selective freewheeling mechanism.
2. Description of the Prior Art
Freewheeling mechanisms are known per se and are also known as directionally-shifted clutches. A freewheeling mechanism has a shaft and an outer ring, and the shaft can also be embodied as a hollow shaft or inner ring. Between the shaft and the outer ring, there are locking elements, which allow a rotation of the shaft relative to the outer ring in one direction, the so-called freewheeling direction, and lock against a rotation of the shaft relative to the outer ring in the opposite direction, the so-called locking direction.
In a selective freewheeling mechanism, the locking elements can be put in a disengagement position, in which they are out of action, or in other words do not lock against a rotation of the shaft relative to the outer ring in any direction. In the disengagement position, the shaft is rotatable in both directions relative to the outer ring. In an engagement position, a selective freewheeling mechanism has the usual function of a freewheeling mechanism; that is, the shaft is rotatable relative to the outer ring in the freewheeling direction and is locked against rotation in the opposite locking direction.
Electromechanical vehicle brakes as wheel brakes for motor vehicles are also known. An electromechanical vehicle brake has an electromechanical actuation device, with which a fiction brake lining can be pressed for braking against a brake body that is fixed against relative rotation to a vehicle wheel. The brake body is typically a brake disk or a brake drum. The actuation device typically has an electric motor and a rotation-to-translation conversion gear that converts a rotary driving motion of the electric motor into a translational motion for pressing the friction brake lining against the brake body. Worm gears, such as spindle gears or roller worm drives, are often used as rotation-to-translation conversion gears. It is also possible to convert the rotary motion into a translational motion by means of a pivotable cam, for instance. A step-down gear, for instance in the form of a planetary gear, is often placed between the electric motor and the rotation-to-translation conversion gear. Self-boosting electromechanical vehicle brakes are also known, which have a self booster that converts a frictional force, exerted by the rotating brake body against the friction brake lining that is pressed for braking against the brake body, into a contact pressure, which presses the friction brake lining against the brake body in addition to a contact pressure that is exerted by the actuation device. Wedge, ramp, and lever mechanisms are known for the self boosting.